For the modern food ordering app, the tip is the price of delivering. It's really a misnomer. More accurately, it should be called a bid, since you're placing a bid on your order and hoping a delivery driver will pick it up.

When you were a delivery driver, were you a W-2 employee? Doordash is not that - it's more like a live service market where you bid for delivery from a driver and Doordash attempts to match your order to a driver, all of whom are self employed (1099). They've got to pay all their vehicle expenses and in theory get something for their time, meanwhile Doordash is a middle-man and trying to squeeze both sides of the transaction. When it works, it is pretty impressive, but mostly it just seems like a Mug's game.